craftgrrl | Simple Blanket Question (Reply)

I checked the memories for quilting posts, and decided to check for some clarification.

I am making a simple blanket for my boy for Christmas. Here is my plan: I have a length of robot printed cotton fabric and a length of red flannel (I prewashed already!). I was going to sew them together with a layer of batting in the middle, then put some thread ties so the batting does not shift. But I have some questions:

1. Which do you prefer poly or cotton batting? Any brand? Is it better to buy it in a package, or to buy off the big bulk rolls at Joanns?
2. How do you figure out how much batting to use? (I was thinking of getting it all cut out and pinned, then measuring the fabric to find an amount)
3. Is it best to sew the batting to the back before putting the front and back together?
4. From the memories, it seems that cotton batting should be prewashed. Does this mean I can just toss it in my washer, then dryer? Or should it be tied in a pillowcase? Or handwashed?
5. Quilt binding - yes or no? For this is seems more decorative than useful. All I saw at Joanns was the silky blanket binding, so I'd want to find the cotton kind instead.

Thanks so much! This is my big project this year, and I need to get cracking!